The growth of wireless data traffic is steady and it is anticipated that current frequency spectrum used for wireless operators will not be sufficient to meet the demand for wireless data traffic. Many countries, including the United States and members of the European Union, are working to repurpose underutilized blocks of spectrum so that the spectrum can be shared between incumbent users, also known as primary users, and secondary commercial users. However, if primary users and secondary users transmit and receive signals without coordination, interference between primary and secondary users which is separate from the co-channel interference within primary users systems and secondary users systems may be present.